Electrosurgery is commonly used to cauterize, cut and/or coagulate tissue. In typical electrosurgical devices, RF electrical energy is applied to the tissue being treated. Local heating of the tissue occurs, and, depending upon the waveform of the applied energy and the electrode geometry, the desired effect is achieved. By varying the power output and the type of electrical waveform, it is possible to control the extent of heating and, thus, the resulting surgical effect. For example, a continuous sinusoidal waveform is best suited for cutting, while a waveform having periodically spaced bursts of a partially rectified signal produces coagulation.
In bipolar electrosurgery, the electrosurgical device includes two electrodes. The tissue being treated is placed between the electrodes, and the electrical energy is applied across the electrodes. In monopolar electrosurgery, the electrical excitation energy is applied to a single electrode at the surgical site, and a grounding pad is placed in contact with the patient. The energy passes from the single monopolar electrode through the tissue to the grounding pad.
While tissue heating is the mechanism by which the various surgical treatments are realized, it can also cause various obstacles to optimum procedure performance. For example, the heat causes tissue fluids to evaporate. As the tissue is desiccated, the electrical resistance of the tissue increases, making it increasingly more difficult to supply adequate power to the tissue. Eventually, the resistance rises to such a high level that it is impossible to continue the procedure. This is such a well-known and common problem in prior electrosurgical devices that surgeons have become accustomed to it and have tailored their procedures to minimize its effects. Typically, surgeons operate prior electrosurgical devices at a very low power level. This prevents the electrode and the adjacent tissue from becoming too hot too fast. Unfortunately, it also requires the surgeon to perform the procedure much more slowly than he would if he could operate the device at full power. As a result, the procedure takes much longer, requiring more operating room time and longer exposure of the patient to dangerous anesthetics.
Heating also causes charring of the tissue. Like desiccated tissue, charred tissue is of very high resistance. Therefore, as the surface of the tissue being treated becomes charred, it becomes difficult, and eventually impossible, to continue delivering power to the tissue as desired. Once again, to avoid the problem, surgeons perform procedures much more slowly than is desirable.
Electrosurgical procedures are also hindered by adherence of tissue to heated electrodes. During electrosurgery, the heated tissue tends to transfer heat to the electrodes. As an electrode becomes hot, tissue tends to stick to it, resulting in various complications. First, the tissue stuck to the electrode can have a high resistance and can therefore hinder delivery of power to the tissue. In prior devices, while performing a procedure, a surgeon must periodically remove the device from the patient and clean it before continuing. In addition, surgeons can perform the procedure at reduced power settings to reduce tissue adherence and thus the frequency of cleanings.
Tissue sticking can also cause unnecessary bleeding. During electrosurgical procedures, the tissue being treated often heats the electrode such that, when the electrode is removed from the tissue, a portion of the tissue sticks to the electrode and is torn away, which likely results in bleeding. Thus, as the surgeon is attempting to cauterize in order to stop bleeding, he is actually causing more bleeding. He must therefore make repeated attempts to cauterize the area, first cauterizing, then tearing away tissue, then recauterizing the torn tissue, etc. Once again, in an attempt to alleviate the problem, surgeons will typically operate at low power, resulting in a procedure requiring much more time to complete than is desirable.
Another problem caused by heated electrodes is the creation of smoke in the proximity of the surgical site. As a result, the surgeon""s visibility is reduced, and he must periodically interrupt the procedure to allow the smoke to dissipate.
It has been recognized that cooling the surgical site during electrosurgery would be desirable. In response, systems have been developed which flush the surgical site with fluid during surgery. However, this results in much more steam being created at the surgical site and the associated reduction in visibility. Also, the fluid introduced at the site must be aspirated as the procedure is performed.
U.S. Pat. No. 5,647,871 introduced a high conductivity device, a heat pipe, to conduct heat from the heated electrode to a heat sink. The heat sink maintains the heat pipe temperature below 80xc2x0 C., the sticking point of tissue to metal.
It has been determined that for certain heat pipe diameters and lengths, the heat pipe itself can store and transfer sufficient heat to the environment, without the use of an additional heat sink, to maintain its temperature below the required 80xc2x0 C.
There are several advantages to using the heat pipe to dissipate heat, rather than using a heat sink. First, elimination of the heat sink makes the device more compact, less expensive and therefore practical for sale. Second, the ideal electrosurgical pencil device would operate between 60 and 80xc2x0 C. The lower temperature is the initiation of coagulation and the upper temperature is the sticking point. The addition of the heat sink lowers the operating temperature of the heat pipe which can negatively affect the depth of penetration of the thermal effect. If the pencil tip is too cold, then there may be a delay in the onset of coagulation and the effect of the coagulation will be deeper in the tissue than may be desired. The present invention passively controls the temperature of the pencil so that the temperature remains closer to the desired set point. Also, the addition of a heat sink adds thermal inertia to the device. This slows the rise time of the heat pipe temperature and also slows the drop in temperature after energy application is stopped. Both of these situations are undesirable. Removal of heat sink removes the thermal inertia.
The invention relates to an electrosurgical device having an electrode and a heat pipe for conducting heat from the electrode. Substantially all heat conducted from the electrode through the heat pipe is dissipated along the length of the heat pipe. The distal end of the heat pipe includes an outer surface having a nickel plated layer or a gold plated layer. The heat pipe is covered along its length by a sheath. The sheath can be formed of a heat shrink tubing. The heat pipe can be attached to and extend from a handle.
The heat pipe has a surface area between approximately 11.0 cm2 (1.71 in2) and 15.0 cm2 (2.33 in2). The heat pipe also includes a diameter of 3 mm (0.12 inches) and a length between approximately 9 cm (3.5 inches) and 11.5 cm (4.5 inches). The heat pipe has a thermal time constant less than 60 seconds and preferably has a thermal time constant less than 30 seconds.